pickerd1

I am considering merging two SRAM PG 1030 cassettes together.
The first is 11,12,14,16,18,21,24,28,32,36
The second is 12,13,14,15,16,17,19,21,23,26

My idea is to make a 11, 13, 15, 16, 17, 18, 19, 21, 28, 36

Is this feasible?

I think the 11 and 13 will be ok and so will the 15, 16, 17, 18, 19.

The 21, 28, 36 has large jumps between sprockets - I suspect this is ok given some of the megarange cassettes on the market - any comments?

I biggest concern is splitting the spider to fit the 21, 28, 36. Will this work?
Problems I can see: will be sprockets all fit the same spider? Will the sprockets fit back on the spider, e.g. are they riveted on?

Any ideas / comments welcomed?

KenCarlson

The phasing of the teeth of each cassette cog are designed so that shifting is smooth between two cogs that are designed to go next to each other. The tooth shaping is designed so that certain teeth more easily allow the chain to move from one cog to the next and the chain link line up to land exactly in the teeth of the next cog. Switching around the cogs will ruin that design, so expect shifting to suffer a bit, the chain might skate across the teeth for a little bit until it drops into place. But from what I hear about people's practical experience is that it's not as bad as it might sound, since all that is doing would be going back to the days of before hyperglide shifting.

Shimano cassettes have the last three large cogs riveted together, so I assume SRAM are the same way. I know you can drill out the rivets to separate the cogs for mixing and matching, so I believe that should work for you.

I would guess that the large shifts from 21 to 28 to 36 would work, but I have no practical experience other than knowing that megarange cassettes actually work. But for my taste, jumps that big would be ridiculously large. I run a 12/27 cassette on my road bike, and the 21-24-27 jumps are too big for my taste, and I'm thinking of switching to a 12/25 cassette. But of course your opinion on that may differ if you want that cassette for major hill climbing. If hill climbing is your goal, personally, I would go with a triple with a low granny ring before resorting to a wide range cassette like what you are proposing. But of course the cassette experiment is much cheaper than a triple to try out if you have a double. If you already have a triple, then it might be worth thinking about reducing the size of your granny ring for climbing.

-Ken

FBinNY 

+1, yes it will work, but the phasing will be off, so shifting may not be as crisp. OTOH you spend more time riding than shifting, so if it gives you gearing more suited to your needs it's probably a decent trade off.

pickerd1

Thanks for your replies.
So it seems feasible.
I can see the potential problem of the large jumps as they may spoil what ever rhythm I have at that point in a climb. It has been mentioned to me that ratio or gear inches can be misleading and that looking at percentage change between gears is the best method to assess this. Any comments on this?
My only concern is after drilling out the rivets on the spider / carrier to remove the large sprockets I will have to re-attach the new ones - can the rivets be replaced with allen key screws or are new rivets needed? If so can these be purchased?

hueyhoolihan

the rivets were only there to assist in initial assembly at the manufacturing plant. they aren't necessary for use, the splines on the freehub prevent unwanted rotation of cogs. i could be wrong of course.

i just use gear inches, further calculations to create percentage change are unnecessary IME. differences between gear inches are obvious to me.

FBinNY 

From the description, I believe that the OP is using cassettes with shared spiders on the larger sprockets, the way better Shimano and Campy cassettes are made.

This is common and caluable on larger sprockets because the added torque on the 2mm wide spline would cut into the freehub body.

pickerd1

You are right FBinNY I am using a cassette with a common carrier for the larger sprockets. I think the top 3 are all attached to the spider. This means the rivets are critical.

Can they be replaced?

KenCarlson

You shift gears on a multi-speed bike to maintain your ideal cadence for the speed at which you are going. About a 10% range of cadence is a typical rule of thumb for lots of people's cadence tolerance. That's the long way of saying that percentage changes between gears is what is important. 21 -> 23 gear change is (23-21)/21 = 9.5%, where 21 -> 28 is (28-21)/21 = 33%. So the 21 to 28 cog shift is roughly equivalent to a shift between a typical big chainring and typical middle chainring (53 - 39)/39 = 36%. That's why I was suggesting looking at your granny gear (if you have triple chainrings), so that you can shift to a low granny ring for climbing, but you could still have a cassette with more closely spaced cogs to achieve that 10% change between gears. But don't put too much emphasis on maintaining a 10% change between cassette cogs. Millions of people run cassettes with much greater percentage changes between their cogs, it's just that the tooth count gaps you are proposing are greater than what most people would be comfortable with.

-Ken

FBinNY 

So there are two issues. The first and limiting one is whether the same spider is used on both cassettes. If so, it may be possible to replace the rivets with screws and nuts, possibly aided with an adhesive. The key here would be the height of the spider holes compared to the next smaller sprocket.

Grand Bois

You are not wrong.

achoo

This is an image from SRAM's site of a cassette like the ones I think the OP is wanting to rearrange:



Given that image, even if the spider is the same on both cassettes, I don't think it would be easy at all to come up with a way to reassemble the cogs to the spider in a way that would both provide for the clearance needed and be reliably strong enough to hold up under load.

pickerd1

achoo - yes that's the one
And I think it will be very difficult to change the present 28, 32, 36 to 21, 28, 36.
Replacing the rivets with nuts and bolts is probably prohibited by available space.
And I don't expect the 21 tooth sprocket fits on a spider.
Back to the drawing board.

I think KenCarlson's granny ring idea may be the only way to go?

Eric S.

I mixed up some SRAM cogs awhile back without realizing that tooth orientation was an issue. The Franken-cassette doesn't suffer from any shifting issues; maybe I got lucky with my choice of cogs, though.

achoo

What would you use the cassette your trying to put together for?

If you really want the tight gearing through the 15-19 cogs, and need the 32 for a bailout, maybe just punt on the 11 or 12 and get a junior cassette and match it with the 28-32-36 spider? You'd lose the 11 or 12, but do you really need that?

fietsbob

Older Shimano cassettes were individual cogs with 3 bolts and spacers ..
right near the splines .. 7 speed K cassetes were fine .. 29 34 the last 2..

quest for weight reduction eliminated that .. & more 'speeds' ..

hueyhoolihan

apparently i'm wrong... again.

FBinNY 

Not totally. You were right as it applied to the more common pinned, loose sprocket Sram cassettes. It's just that these are different models. As is so often true, the devil is in the details.

pickerd1

achoo
I really like the idea of a 36 as a bail out and I would like close ratio in the 15 to 19 range. This suits my riding style as a never want to push the bike and I got used to close ratios years ago when I was riding a road bike.
This junior cassette sounds interesting - what is it?

Thanks

Bill Kapaun

Regarding % of change between gears:
Basically YOU have to determine what best fits your need.
Personally, I like large jumps between the lower gears since they are just to get me up to my "cruising" range. I spend very little time in them.
Once up to "cruising", I like very small jumps so I can maintain the narrow cadence range which works for me. (emphysema)
My riding is pretty much on flat, smooth pavement. If I was "doing hills", I'd probably want a more even spread.

hueyhoolihan

thanks, you're right, i didn't read the fine print. i know better.